1. Field of the Invention
The present invention relates to a polymer blend film obtained using a cyclic olefin resin.
2. Description of the Related Art
A polarizing plate is manufactured by laminating a protective film on both sides of a polarizing film obtained by oriented adsorption of iodine or a dichroic dye to polyvinyl alcohol. As the protective film, that composed mainly of cellulose triacetate is popularly used because of its characteristics such as toughness, flame retardancy and high optical isotropy (low retardation value). A liquid-crystal display device is made of a polarizing plate, a liquid crystal cell, etc. A liquid-crystal device having a high display quality is achieved by inserting an optical compensation sheet (which may also be called “optical compensation film) between the polarizing plate and liquid crystal cell of the device as described in JP-A-8-50206 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
The cellulose triacetate film is very hygroscopic and therefore has poor dimensional stability. It is likely to undergo changes in optical compensation performance or separate from the polarizing film. In addition to these problems, the cellulose triacetate film hardly exhibits optical characteristics even by stretching.
A cyclic olefin film has attracted attentions as a film capable of overcoming the shortcomings of the cellulose triacetate film in hygroscopicity or moisture permeability and development of it as a protective film for a polarizing plate is now performed utilizing a heat melting or solution casting film formation method. The cyclic olefin film exhibits high optical characteristics and moreover, a change in the optical characteristics due to temperature or humidity is small so that it is now developed as a phase difference film (JP-A-2003-212927, JP-A-2002-114827 and JP-A-2007-9010)
The cyclic olefin resin film however has drawbacks such as low surface hardness, low elastic modulus, and brittleness. Another drawback of the cyclic olefin resin is that it achieves an adequate Re or Rth value by stretching but the value cannot be controlled easily and orientation of molecules becomes uneven only by slight stretching, which may lead to unevenness when the film is arranged in crossed nicols.